This open-label, single arm study will evaluate the safety and efficacy of Tarceva (erlotinib) as first-line therapy in patients with stage IV or recurrent non-small cell lung cancer who harbour epidermal growth factor receptor (EGFR) mutations. All patients will receive Tarceva 150 mg daily orally until disease progression or unacceptable toxicity occurs. At the investigator's discretion, patients may receive Tarceva beyond disease progression.